According to the ipcs manual page: SEGSZ (a,b), is the size of the associated shared memory segment. However, this is misleading. The shared memory segments reported by ipcs are virtual memory segments requested by the user process.
After executing the ipcs -am command, you see information similar to the following:
T ID KEY MODE OWNER GROUP CREATOR CGROUP m 4099 0x58059007 --rw-rw-rw- root system root system SEGSZ CPID LPID ATIME DTIME CTIME 268435456 19792 19792 14:36:33 no-entry 14:36:33
Xwindows is not actually using 256 MB of actual memory, rather, it is using 256 MB of address space inside the linked list of the VMM itself, with the kernel allocating memory to Xwindows dynamically within the stack.
The number reported is hard coded into Xwindows. This cannot be changed. This
is
the way it was designed, and it should not impact your system's
performance. This number is on ALL computers running Xwindows.
[ Doc Ref: 97413915321064 Publish Date: Nov. 13, 2000]